Adaptation

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Adaptation

• Psychology 3106

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Introduction

• Last class we looked at what you might call the
  historical pathways that a behaviour or trait
  can take
• Basically, how you get from one form to another
• You can also look at the adaptive value (fitness
  consequence) of behaviour
• As noted, these are related

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Adaptation A Definition

• An adaptation is a heritable trait that
• Either spread because of Natural Selection and
  has been maintained by selection to the preesnt
• Or
• Is currently spreading relative to alternative
  traits, due to Natural Selection

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More Adaptation

• Nice thing about this definition is that it can
  help us figure out if something is indeed an
  adaptation.
• Does it increase fitness?? That is the question
• What are the costs and benefits?

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Not all traits are adaptations

• The conditions that the trait evolved in may not
  exist
• The trait may be a maladaptive side effect of an
  adaptive trait
• The trait is a maladaptive expression of some
  adaptive trait
• The trait may be an exaptation

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Measuring Fitness

• Sometimes we can get direct measures of fitness
• Gamete production
• Offspring survival
• Rate of copulation
• Fertilized egg production
• Offspring production
• Offspring independence

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Measuring Fitness

• Often we have to go to indirect measures of
  fitness
• Improved locomotion
• Improved access to food
• Improved survival chances
• Improved access to territories
• Better territories

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An Example Mobbing in Gulls

• When you get near a nesting colony of gulls they
  get pretty angry.
• Dive bombing
• Swooping
• Hitting!
• A good guess is that this behaviour is an
  adaptation for defense of their young
• But, as good as it sounds, does mobbing increase
  fitness?

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Mobbing Gulls

• OK, if mobbing is indeed an adaptation then, the
  degree of success experienced by mobbing gulls in
  protecting their eggs should be proportional to
  the degree to which predators are actually
  mobbed.
• Kruuk (1964) tested this prediction.
• Placed 10 hen eggs, every 10 m on a line leading
  from outside to inside a colony
• The ones outside the colony were more likely to
  have been taken

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Kruuuuuuuuuuuuuuuuk (1964)
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Mobbing in Barn Swallows

• Barn Swallows also mob.
• Could be self defense
• Could be mating advertisement
• Could be an alternative to parental care
• Shields (1984) placed a stuffed owl near a colony
  of barn swallows, and took note of who mobbed

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Shields (1984)
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The Comparative Method

• Just as with looking at the history of some
  trait, the question of whether a behaviour is an
  adaptation or not can be (partially) answered
  with the Comparative Method
• We would expect that birds that are cliff nesters
  would not mob, while those that were ground
  nesters would
• Regardless of relatedness

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Convergent and Divergent Evolution

• This is in fact the case
• The common ancestor of Gulls and Barn Swallows
  was ages ago!
• Indeed, some colonial mammals mob!

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Optimality Models

• When does it make sense to use a particular
  strategy?
• When does it make sense to evolve a particular
  strategy?
• Look at the costs and benefits, thugh the use of
  optimality models
• Basically looking at costs and benefits

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Optimality Models

• You might mob some of the predators some of the
  time..
• Top model looks only at costs and benefits
• Bottom model looks at percentage of cautious and
  daring mobbers, they are dependent on each other!

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Criticism of the Adaptationist Approach

• Biggest critic was Stephen J. Gould
• The only palaeontologist ever to appear on The
  Simpsons
• Trait may be maladaptive now, but adaptive then
• The trail may be a maladaptive byproduct of an
  previously adaptive (or presently adaptive) trait

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More Criticisms by that baseball loving commie

• Trait would never have occurred in the past, but
  new wacky conditions make it show up now
• The trait is less than perfect because it is
  constrained by past evolutionary events

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Take that Dinosaur man

• An assumption of adaptationism is that traits are
  adaptive, we then test the prediction.
• It has never been about perfection Steve, I dont
  know what you read
• The point is not to be correct, but to be
  testable and proved wrong. You should have paid
  more attention in Philosophy of Science class.
  Science is not Essentialist!

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Conclusions

• Dont be a rabid adaptationist
• Dont fall for the naturalistic fallacy either!
• Remember, its all about reproductive success in
  the end, so we really need this approach to test
  why something evolved.
• This stuff is all intertwined with the stuff on
  the historical pathways of evolution that we
  talked about earlier